Private equity firm Wasserstein & Co. LP has acquired audio book group Recorded Books LLC for an undisclosed amount.

Recorded Books provides audiobooks, digital content and other services to library, school and retail markets. The company offers more than 13,500 audiobooks, as well as 100,000 e-books. Northwestern Mutual and Lexington Partners are co-investing on the transaction with Wasserstein.

Wasserstein, headquartered in New York, invests in the media, communications, consumer products and water equipment industries. In December, Wasserstein closed a $340 million deal for Globecomm Systems Inc., a satellite communications company. 

Northwestern Mutual is a Milwaukee-based financial services mutual institution. New York-based Lexington Partners manages secondary private equity, with about $20 billion in committed capital.

The target was sold by Haights Cross Communications Inc., an educational and library publisher.